Last night Indian newspapers suggested not all radar units were "awake" (I posted a link). The longer this sad, sorry affair goes on the harder it feels to accept any official statement on face value.
I don't find this that surprising. I remember an analysis of the Bin Laden raid, and one of the reasons the US felt they could sneak in, is that Pakistan did not have much western-facing military radar; India is their only real foe in the region (discounting the US presence in Afghanistan) so most of, and the best, radar assets are pointed east.
I suspect India's strategy is much the same. They don't fear anyone coming in from the east -- most of their assets are directed at Pakistan and to a lesser degree China -- so the military radar there is likely to be inferior and coverage more spotty. The fact that nobody was paying attention to a low-risk area is an embarrassment for India, but not that surprising to me.